Upper part shows composition on the start. And lower part shows what happens when I place in that page a new object - TIFF file with transparency (this black signature). The green color of the photo on the left changes, fades a bit.

When I import regular jpg without transparency - everything is OK.

And one more thing: please notice part of the photo with hairs on the bottom right - it doesn't change the color!! (It doesn't matter that the signature is not overlaping the hairy photo - I've checked that too)

I've checked those two files files (the green one and those hairs) - their properties seems to be identical:

there's no color profile embedded

both 8 bit

both RGB

What elce can I check to solve this problem. Or maybe it's only VIEW of that colors, and they will be the same when printed?

Thanks man, it helped! :) Now - despite the signature is present or not - colours remain the same.

Could You please enlight me a bit more by the way? What is this separation preview for? I know, that I could ask too much - since it's a part of PRINTING MAGIC, told to be the hardest thing to learn in digital world :) - but can You at least put my further investigations in the right direction?

I would be greatful, because those printing matters are hard to explore without a guidance :/